"Geckoprinting" Puts Sticky Gecko Feet to Work

Rather than try to copy a gecko's super-sticky feet, scientists put the real thing to work.

For years engineers have been trying to copy the gravity-defying feet of the gecko, which enable the small lizards to scurry across ceilings and up walls with ease. Tiny toe hairs help to keep a gecko stuck like glue to a surface, but they come right off without leaving a trace, and they're self-cleaning, able to avoid picking up dirt and debris.

But instead of going to all the trouble of reengineering all this, a team in South Korea came up with a new method: just use the geckos' real feet. They say gecko toe pads can be used like stamps, building tiny, unconventional electronic devices. They're calling it geckoprinting. The work appears in the Journal of the Royal Society Interface.

Geckos have leaflike arrays on their feet, each covered in micro- and nanoscale hairs called setae. These hairs can generate adhesive forces that allow geckos to hang upside down on smooth surfaces. What sets them apart from sticky adhesives is that they work mechanically, Kellar Autumn, a professor at Lewis & Clark College and the first to describe how gecko adhesion works, says.

"Tapes are sticky all the time. Gecko-like fibrillar adhesives are only sticky when we need them to be, and are switchable mechanically," Autumn says. "An inward pull along the surface makes them stick, and a push away causes release."

While a graduate student at the University of California, Berkeley, Jongho Lee, now at the Gwangju Institute of Science and Technology in South Korea, helped to devise a gecko-inspired polymer-fiber array that easily attached to and detached from a surface. He and his colleagues wanted to try the real thing, so they detached them from geckos' feet. It doesn't hurt the geckos, Lee says. Scientists can remove the pads with an X-acto knife without harming the animal, and the gecko will regenerate its adhesive pads at its next molt, usually within a month or two.

Lee and colleagues used Locktite glue to attach the setae to a piece of glass, and called this device a stamp. Then they were able to pick up, move, and detach small pieces of silicon and attach them to other surfaces. When they dragged the stamp in the opposite direction, they could disengage it. They gecko-printed silicon wafers onto other silicon wafers, onto the leaf of a leopard plant, and onto the wings and body of a darkling beetle.

Tiny electronic devices could be helpful for a wide range of tasks, but they are tough to produce because silicon chips are delicate and hard to attach to uneven, fragile surfaces. The stamp is a much gentler way of depositing the chips.

The experiment proved that these gecko setae could be an effective way to transfer-print small bits of silicon for minuscule electronics, Lee says. Previous research showed each seta could last through 30,000 on/off cycles, Autumn says.

"It's a great example of the path from basic science discoveries to valuable engineering applications," he says.

It's unlikely large manufacturers will start buying up boatloads of geckos to print microelectronics—the "real thing" is for small-scale projects, Lee says. But that still includes things like balloon catheters, proximity sensors, unobtrusive light detectors, micro-LED light sources, and a lot more. The team gecko-printed some small solar cells to prove that it works. Lee and Autumn would like to build artificial gecko adhesives inspired by the setal stamp but in simpler structures that could be purpose-built for specific tasks.

While imitation may be the sincerest form of flattery, sometimes it's just not enough.

"It is still very challenging to make structures with materials that have similar mechanical or chemical properties comparable to the sophisticated natural structures of natural geckos," Lee says. "I think there is no such thing comparable to natural geckos' adhesive . . . I thought, why we are not using natural geckos? They are still the best smart adhesives."

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